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CHAPTER 5 ADVANCED ACTIVE RECORD: ENHANCING YOUR MODELS
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if you wanted to wrap the users table, you would simply create a subclass of ActiveRecord::Base called User, like this:
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class User < ActiveRecord::Base end
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That s all you really need to have Active Record map the users table and get all the basic CRUD functionality we described in 4. But few models are actually this bare. So far, we ve been leaving our models classes unchanged. That s a good thing, and it speaks to the power and simplicity of Active Record. However, it leaves something to be desired. Most of the time, your models will need to do a lot more than just wrap a table.
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Note If you re familiar with SQL, you re probably feeling that Active Record provides you with only
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simple-case solutions and it can t handle complicated cases. That s entirely untrue. While SQL is useful for highly customized database queries, most Rails projects rarely need to touch SQL, thanks to some clever tricks in Active Record.
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The primary way in which we enhance models is by adding methods to them. This is what s referred to as adding domain logic. With Active Record, all the logic for a particular table is contained in one place: the model. This is why the model is said to encapsulate all the domain logic. This logic includes access rules, validations, relationships, and, well, just about anything else you feel like adding. In addition to all the column-based reader and writer methods you get by wrapping a table, you re free to define your own methods on the class. In fact, an Active Record subclass isn t much different from a regular Ruby class. About the only difference is that you need to make sure you don t unintentionally overwrite any of Active Record s methods (find, save, or destroy, for example). For the most part, though, this isn t a problem. Let s look at a simple example. We re often faced with the problem of having to format data, rather than accessing a model attribute in its raw form. In our events application, we would like to be able to produce a formatted, long title that includes the name of the event, its location, and its date. To accomplish this, all we need to do is define a new instance method that performs the concatenation of those attributes and produces a formatted string. We ll call the method long_title. Add the code shown in Listing 5-1 just before the last end statement in the app/models/event.rb file.
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CHAPTER 5 ADVANCED ACTIVE RECORD: ENHANCING YOUR MODELS
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Listing 5-1. Custom long_title Method, in app/models/event.rb
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class Event < ActiveRecord::Base #... def long_title "#{title} - #{location} - #{occurs_on}" end end
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We ve just created an instance method on the model; that is, we ve told the Event model that it s now endowed with a new attribute called long_title. We can address long_title in the same way as we would any other method on the class. Let s open an irb session and try this on the console. From your terminal window, start up the Rails console with the following command:
$ ./script/console
This should drop you at a simple irb prompt with two right arrows and a blinking cursor. From here, we ll find an event and call the long_title method.
>> Event.find(:first).long_title => "Tiki Party - Hampton's Apartment - 2007-09-02"
So you see, there is no difference between the methods that Active Record creates and those we define ourselves. Here, instead of just asking the model for one of the attributes garnered from the database column names, we ve defined our own method called long_title, which does a bit more than the standard title method. The methods you add to your models can be as simple as returning true or false, or as complicated as doing major calculations and formatting on the object. The full power of Ruby is in your hands to do with as you please. Don t worry if you don t feel comfortable adding your own methods to models just yet. The important part to note from this first section is that Active Record models are regular Ruby objects that can be augmented, modified, played with, poked, and turned inside out with sufficient Ruby-fu. Knowing this will be extremely helpful in being able to pull back the curtain and understand the advanced features of Active Record.
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